An apparatus for the mixing of at least two reactive synthetic resin components to form a hardenable or settable mixture which can be discharged into a mold, as described in German patent document DE-PS 23 27 269, has a cylindrical reaction chamber into which the synthetic resin components are injected and from which all residues of the reactive synthetic resin mixture ca be discharged by a reversibly movable mixing-chamber piston which can be displaced within this chamber.
This apparatus is provided with a cylindrical calming chamber into which the mixing chamber is discharged and which lies at an angle to the longitudinal axis of the mixing chamber, namely, a right angle, to form the turbulent mixture discharged from the mixing chamber into a quiescent mixture before it is discharged into a mold cavity. The calming chamber also is provided with a piston or plunger which is reversibly displaceable and can drive all residues of the mixture from this chamber into a mold cavity, i.e. through the outlet of the calming chamber.
Mixing heads of this type require control of the pressure in the mixing chamber by the throttling of the mixing chamber outlet as described, for example, in the German patent document DE-PS 31 20 482. In this system, the piston or plunger of the calming chamber forms an obstructing piece at its front end directly adjacent the mixing chamber outlet and in an intermediate position in which the calming-chamber piston can be arrested. A disadvantage of this kind of throttling approach is that the output rate, i.e. the flow per unit time, through the mixing head is restricted by the throttling operation.